Synthetic resins such as polymethyl methacrylate resin, polycarbonate resin, polystyrene resin, cyclic polyolefin resin, polyethylene terephthalate resin, and triacetyl cellulose resin have advantageous properties including light weight, high transparency, and high workability, and therefore, these synthetic resins are recently finding wide applications in the field of optical disks such as CD and DVD, display windows of liquid crystal and EL panels, and various functional films.
In order to improve scratch resistance of such surface, a transparent hard coating having scratch resistance is generally formed on the medium on the side of the read and/or write beam incidence. The hard coat is formed by coating the surface of the medium with a composition containing a compound having at least two photoreactive groups such as vinyl group and (meth)acryl group in the molecule, a siloxane compound having a basket structure produced by hydrolyzing and condensing an alkoxysilane having a photoreactive group such as vinyl group and (meth)acryl group in the presence of a basic catalyst (JP-A 2002-363414 and JP-A 2004-143449: Patent Documents 1 and 2), and a reaction product of an alkoxysilane having a photoreactive group and a colloidal silica; and curing the thus formed coating by irradiating with an active energy beam such as UV beam. However, the photoreactive group mainly employed in these hard coating had been (meth)acryloxypropyl group, and accordingly, the scratch resistance was insufficient, and the resistance to smudges such as fingerprints and removability of oil-base felted markers by wiping could not be expected.
JP-A 2005-179587 (Patent Document 3) discloses use of a siloxane compound containing (meth)acryl group for the photoreactive group in the silica based coating. However, the siloxane compound is used in this case not for the production of a coating composition for forming a hard coating, but for the formation of a low k interlayer dielectrics having flatness. More specifically, the siloxane compound is used for the purpose of forming voids in the layer by curing the siloxane compound and decomposing and removing the organic group by heating, UV/EB irradiation, or plasma treatment.
When such products are used, various types of smudges and fingerprints deposit on the surface of such resin, and since such smudge and fingerprint deposition is not preferable, the surface of an optical information medium is often subjected to an adequate surface treatment to thereby improve the smudge proof property, reduce fingerprint deposition, and improve removal of the fingerprints. For example, attempts have been made to provide a variety of water and oil repellent treatments on the surface of an optical information medium.
With regard to improvement of smudge proof property, Japanese Patent No. 3603133 (Patent Document 4) discloses a siloxane compound having a basket structure produced by hydrolyzing and condensing an alkoxysilane having a polymerizable functional group and an alkoxysilane having a perfluoroalkyl group in the presence of a basic catalyst. The coating formed by curing a composition containing this compound has an increased contact angle with oleic acid, and improvement in the smudge proof property is expectable. This coating, however, suffers from insufficient removability of oil-base felted markers by wiping as well as a markedly reduced abrasion resistance.